How can I change the frame range in an alembic file?
If I got what you ask, here is a way that seems to work: I created a simple blender cloth sim, a cube with hooked vertices, 50 frames long. Then, exported that as alembic.

After I opened a new default blender file, deleted the default cube, and imported the above .abc file.

I got the object in my new file, and the animation worked thanks to a "Mesh Sequence Cache" modifier I found for my object; also my new file frame range has become 1-50 (it was, as default, 1-250).

Now, while my blender frame was 1, I checked the modifier's "override frame" option, and set a keyframe for frame "1". Then I moved to blender frame 50, and set a keyframe for the modifier's "frame" option to "50".



Now, in the NLA editor I have a new "action" 



that can be converted ("pushed") to a "strip" using the double arrow button. 



After that, you get a strip, which can be moved anywhere in the timeline...



here it is starting at frame 40, and last until frame 90... (of course before I extended the blender frame range to somewhat higer...)